The utility model relates to a locking device for continuous casting crystallizers to solve the weaknesses of locking devices for on-line width-adjusting crystallizers that the insufficient inherent stress easily causes seams during production etc. Technical measures: the utility model comprise an upper oil cylinder (1), a lower oil cylinder (2), an upper cylinder piston rod (3) installed in the upper oil cylinder (1), a lower cylinder piston rod (4) installed in the lower oil cylinder (2), end caps (5) installed on the upper oil cylinder (1) and the lower oil cylinder (2), springs (6) respectively installed on the upper cylinder piston rod (3) and the lower cylinder piston rod (4), wherein threads (7) are made inside the ends of the upper oil cylinder (1) and the lower oil cylinder (2); adjusting sleeves (8) and springs (8) that are installed in combination with the threads (7) are provided on the ends of the upper cylinder piston rod (3) and the lower cylinder piston rod (4) and are compressed by the adjusting sleeves (8). Adjustment of inherent stress for the locking device is convenient and stable so that on-line width-adjusting crystallizers do not easily cause seams, and the operation becomes safer and more reliable.